Quick facts about apple maggot
The most important insect pest of Minnesota-grown apples is the apple maggot (Rhagoletis pomonella), sometimes called the "railroad worm.”
- It feeds on apples and large crabapples.
- Appears in early July and is active until September. Peak activity occurs from late July through early August.
- Heavily infested fruit is distorted, inedible and suitable only for cider or animal feed.
How to identify apple maggot
The adult fly is ¼ Inch long, smaller than a common housefly.
- It has characteristic dark markings on the clear wings and a conspicuous white spot where the thorax joins the abdomen.
- Has three (male) or four (female) white stripes on the abdomen.
Life cycle of apple maggot
Adult apple maggots begin to come out of the soil starting about July 1, continuing through most of the summer.
- Adult flies often leave and feed outside the orchard, in wooded or brushy areas.
- They return to lay eggs just under the skin of apples.
- Each female fly can lay hundreds of eggs.
- Once eggs hatch, larvae feed for three to four weeks.
- When apples drop to the ground, the larvae transform into pupae in the soil.
- Pupae spend the winter underground, emerging as adults the following summer.
Damage caused by apple maggot
Apple maggot lays eggs in the fruit and the fruit becomes pitted and misshapen.
Each "sting” or hole created by the female fly as she lays an egg, forms a tiny spot or dimple.
Pulp breaks down, discolors and starts to rot as a result of maggots (larvae) tunneling through the flesh. Larvae are rarely seen.
How to protect your trees from apple maggot
Keep your garden clean
Clean gardens have fewer apple maggot problems.
- Frequently pick up and remove any apples that fall during the growing season and after harvest.
- Place these apples in the trash or send them to a municipal composting site.
- Do not compost them in your yard.
Apple maggot flies can enter the planting from outside. Only maintaining a clean garden will not prevent the attack of apple maggots.
Thin the fruit (remove some apples from the trees) in early to mid-June.
- Enclose each apple in a plastic sandwich bag, either a zipper closure bag or a plain bag closed with staples.
- Snip the bottom corners off each bag with a pair of scissors to leave a small opening for water to run out.
- At harvest, remove the bag.
Bagging fruit may take a few hours, but, the apples are protected from apple maggots for the rest of the season.
Bagging is easy to do if you have a small to medium-sized tree that can be managed from the ground or a short ladder.
If you have a tall tree, you may choose to bag only the fruits that are easy to reach, and let the apple maggots have the higher fruits.
Using sticky traps
The trap-out method uses sticky traps to capture apple maggot females that attempt to lay eggs on the fruit.
Apple maggot traps are red spheres coated with tanglefoot, a sticky substance that permanently holds insects.
Some options for apple traps are:
- wooden or plastic spheres painted red
- red plastic spheres designed and sold specifically for this purpose
- store-bought large, red, fresh apples
Whichever type of trap you choose, the spheres or apples should be at least 3 inches in diameter and bright red.
- Hang up wooden spheres with an eye screw and a wire hook. Hang up fresh apples by skewering the apple with a coat hanger and bending the excess wire into a hook.
- Hang scent lures (that smell like the apple fruit) with your traps to make them more attractive to flies.
Hang one trap per 100 fruit (after thinning) in each tree.
- One or two spheres for small trees and five or more traps for larger trees.
- Place at least one trap on the side of the tree that faces any wooded or brushy area.
- A second trap should hang on the south side of the tree.
If there are apple or hawthorn trees in wooded or landscaped areas nearby, you may want to hang traps in these trees as well, to further reduce apple maggot pressure.
- Hang traps in the trees by the end of June, to catch the apple maggot flies as they first attempt to lay eggs.
- Remove any leaves or fruit touching the traps.
- Check all the traps weekly and, as needed, clean off the tanglefoot-coated insects, and/or apply more tanglefoot.
Check for the presence of apple maggots using sticky red spheres.
- Check the trap frequently.
- If you do not use a scent lure, spray for apple maggots as soon as you catch a single adult.
- If you hang a trap with a lure, wait until you have caught a total of five flies, whether they are all caught at once or one at a time.
Effective pesticides available for apple maggot control are: esfenvalerate, carbaryl and spinosad.
At the end of the spray interval (as given on the pesticide label), clean any insects off the trap, reapply tanglefoot if needed, and begin checking the traps every day or two as before.
- Spray again and repeat the whole process, as needed.
- You might have to spray for apple maggot three or four times per season.
Fortunately, the number of apple maggot adults reduces as the season progresses, and you should be able to stop spraying sometime in August.
CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Remember, the label is the law.
Be sure that the fruit/vegetable you wish to treat is listed on the label of the pesticide you intend to use. Also be sure to observe the number of days between pesticide application and when you can harvest your crop.
Using kaolin clay
Kaolin clay, can discourage apple maggot flies and other insects from laying eggs in apple plantings.
- Apply in a visible layer to all surfaces of the tree, leaves and fruit. This acts as a visual and physical repellent to insects.
- Apple maggot females are attracted to the red color of ripening apples, so a grayish-white apple is not attractive to them.
- The layer of clay on fruits repels many insects and they may leave immediately.
The clay washes off easily even in moderate rain and may not provide enough coverage. As fruits expand, coverage must be renewed frequently.
This method is not very reliable and effective, due to the difficulties in maintaining good coverage.
Reviewed in 2018